The intent of this application is to request funds for the training of minority students in the field of developmental neurobiology. Students will be involved in experiments designed to examine factors that regulate the expression of neurotransmitter phenotypes in developing neurons of the central nervous system (CNS). In our current MBRS grant period we have established a model for such developmental studies by characterizing a unique population of monoaminergic neurons in the embryonic chick spinal cord. These neurons are unique in that they express most characteristics of the dopamine (DA) transmitter phenotype, yet in vivo, these cells do not synthesize DA. However, in pilot studies involving tissue culture and microsurgical lesioning procedures, we have demonstrated that these cells can be experimentally manipulated to produce DA. This plasticity in transmitter synthesis ability serves as the basis for experiments to define developmental processes that may contribute to the regulation of neurotransmitter phenotype expression. This proposal includes the following specific aims: (1) To investigate whether descending brainstem afferents modulate or regulate the ability of spinal cord neurons to synthesize DA. (2) Based on preliminary evidence, to further examine whether the influence of brainstem cells on spinal cord neurons is related to any particular transmitter phenotype of neurons that project to the cord. (3) To describe characteristics of "trophic interactions" between target cells and their afferents by determining the specificity of these interactions in relation to selected transmitter phenotypes, or to the appropriateness of the afferent input. The exposure of undergraduate minority students to the exciting field of developmental neurobiology and to current in vitro and in vivo experimental techniques to be used in the proposed studies will hopefully encourage their consideration of continuing their education and training for careers in biomedical research.